Photovoltaic cell having a coupled expanded metal article

ABSTRACT

A method comprises providing an expanded metal article having a plurality of first segments intersecting a plurality of second segments thereby forming a plurality of openings. The expanded metal article has a surface comprising a plurality of solder pads. A semiconductor material with a top surface and a bottom surface is provided, the bottom surface having a plurality of silver pads and the top surface serving as a light-incident surface of the photovoltaic cell. At a plurality of soldering locations, a majority of the plurality of solder pads on the surface of the expanded metal article is electrically coupled with the plurality of silver pads on the bottom surface of the semiconductor material. Also disclosed is a photovoltaic cell resulting from this method.

RELATED APPLICATIONS

This application is a continuation-in-part of International PCTApplication No. PCT/US 15/32622, filed on May 27, 2015 and entitled“Photovoltaic Cell Having a Coupled Expanded Metal Article”; whichclaims priority to U.S. Provisional Patent Application No. 62/014,950,filed on Jun. 20, 2014 and entitled “Photovoltaic Cell Having a CoupledExpanded Metal Article”; all of which are hereby incorporated byreference for all purposes.

BACKGROUND

A solar cell is a device that converts photons into electrical energy.The electrical energy produced by the cell is collected throughelectrical contacts coupled to the semiconductor material, and is routedthrough interconnections with other photovoltaic cells in a module. The“standard cell” model of a solar cell has a semiconductor material, usedto absorb the incoming solar energy and convert it to electrical energy,placed below an anti-reflective coating (ARC) layer, and above a metalbacksheet. Electrical contact is typically made to the semiconductorsurface with fire-through paste, which is metal paste that is heatedsuch that the paste diffuses through the ARC layer and contacts thesurface of the cell. The paste is generally patterned into a set offingers and bus bars which will then be soldered with ribbon to othercells to create a module. Another type of solar cell has a semiconductormaterial sandwiched between transparent conductive oxide layers (TCO's), which are then coated with a final layer of conductive paste that isalso configured in a finger/bus bar pattern.

In both these types of cells, the metal paste, which is typicallysilver, works to enable current flow in the horizontal direction(parallel to the cell surface), allowing connections between the solarcells to be made towards the creation of a module. Solar cellmetallization is most commonly done by screen printing a silver pasteonto the cell, curing the paste, and then soldering ribbon across thescreen printed bus bars. However, silver is expensive relative to othercomponents of a solar cell, and can contribute a high percentage of theoverall cost.

To reduce silver cost, alternate methods for metallizing solar cells areknown in the art. For example, attempts have been made to replace silverwith copper, by plating copper directly onto the solar cell. However, adrawback of copper plating is contamination of the cell with copper,which impacts reliability. Plating throughput and yield can also beissues when directly plating onto the cell due to the many stepsrequired for plating, such as depositing seed layers, applying masks,and etching or laser scribing away plated areas to form the desiredpatterns. Other methods for forming electrical conduits on solar cellsinclude utilizing arrangements of parallel wires or polymeric sheetsencasing electrically conductive wires, and laying them onto a cell.However, the use of wire grids presents issues such as undesirablemanufacturing costs and high series resistance.

Furthermore, in Babayan et al., U.S. Pat. Nos. 8,569,096 and 8,936,709,which are owned by the assignee of the present application and areincorporated in their entirety by reference herein, electrical conduitsfor semiconductors such as photovoltaic cells are fabricated as anelectroformed free-standing metallic article which are subsequentlyattached to a semiconductor material. The metallic articles are producedseparately from a solar cell and can include multiple elements such asfingers and bus bars that can be transferred stably as a unitary pieceand easily aligned to a semiconductor device. The elements of themetallic article are formed integrally with each other in theelectroforming process. However, the metallic article is manufactured inan electroforming mandrel, which, while generating a patterned metallayer that is tailored for a solar cell or other semiconductor device,requires additional equipment and cost.

Therefore, there is a need in the industry for low cost methods forattaching electrically conductive elements to the surface of asemiconductor material to thereby form a photovoltaic cell.

SUMMARY

The present invention relates to methods of forming a photovoltaic cell.In some embodiments, a method includes providing an expanded metalarticle having a plurality of first segments intersecting a plurality ofsecond segments thereby forming a plurality of openings. The expandedmetal article has a surface comprising a plurality of solder pads. Asemiconductor material with a top surface and a bottom surface isprovided, the bottom surface having a plurality of silver pads and thetop surface serving as a light-incident surface of the photovoltaiccell. At a plurality of soldering locations, a majority of the pluralityof solder pads on the surface of the expanded metal article iselectrically coupled with the plurality of silver pads on the bottomsurface of the semiconductor material.

In some embodiments, a method for forming a photovoltaic cell includesproviding an expanded metal article having a plurality of first segmentsintersecting a plurality of second segments thereby forming a pluralityof openings. The expanded metal article further includes a plurality ofcuts, each cut in the plurality of cuts creating a discontinuity in theexpanded metal article. A semiconductor material is provided, thesemiconductor material having a bottom surface comprising a plurality ofsilver pads. A top surface of the semiconductor material serves as alight-incident surface of the photovoltaic cell. The expanded metalarticle is electrically coupled at a plurality of soldering locations tothe plurality of silver pads on the bottom surface of the semiconductormaterial, to form the photovoltaic cell.

A photovoltaic cell is also disclosed, which includes an expanded metalarticle and a semiconductor material. The expanded metal article has aplurality of first segments intersecting a plurality of second segmentsthat form a plurality of openings. The expanded metal article furtherincludes a plurality of cuts, where each cut in the plurality of cutscreates a discontinuity in the expanded metal article. The semiconductormaterial has a bottom surface comprising a plurality of silver pads. Atop surface of the semiconductor material serves as a light-incidentsurface of the photovoltaic cell. The expanded metal article iselectrically coupled at a plurality of soldering locations to theplurality of silver pads on the bottom surface of the semiconductormaterial.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the presentinvention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Each of the aspects and embodiments described herein can be used aloneor in combination with one another. The aspects and embodiments will nowbe described with reference to the attached drawings.

FIG. 1 shows an embodiment of an expanded metal article used to form aphotovoltaic cell, in accordance with some embodiments.

FIG. 2 shows a top view of a formed photovoltaic cell, in accordancewith some embodiments.

FIG. 3 shows a bottom view of an embodiment of a formed photovoltaiccell, in accordance with some embodiments.

FIG. 4A is a plan view of an expanded metal article with cuts toaccommodate thermal expansion, in accordance with some embodiments.

FIG. 4B is a detailed view of FIG. 4A.

FIG. 5 is a plan view of an example photovoltaic cell onto which anexpanded metal article with cuts has been mounted.

FIG. 6 is a perspective view of a metal cutting assembly, in accordancewith some embodiments.

FIG. 7 shows the metal cutting assembly of FIG. 6, with an expandedmetal material inserted.

FIG. 8 shows the metal cutting assembly of FIG. 7, with the expandedmetal material held between a holding plate and a receiving plate of theassembly.

FIG. 9 shows the metal cutting assembly of FIG. 7 after cuts have beencreated in the expanded metal material.

FIG. 10 is a flowchart of methods for forming a photovoltaic cell, inaccordance with embodiments of the present disclosure.

It should be understood that the above-referenced drawings are notnecessarily to scale, presenting a somewhat simplified representation ofvarious features illustrative of the basic principles of the disclosure.The specific design features of the present disclosure, including, forexample, specific dimensions, orientations, locations, and shapes, willbe determined in part by the particular intended application and useenvironment.

DETAILED DESCRIPTION

The present disclosure relates to photovoltaic cells comprising attachedexpanded metal articles.

According to some embodiments, the method comprises the step ofproviding an expanded metal article, providing a semiconductor material,and electrically coupling them. The term “expanded metal article” refersto metallic articles prepared by a known process in which metal in theform of a sheet or plate is simultaneously slit and stretched (i.e.,expanded) in defined patterns to produce a metallic article having acontinuous mesh or grid-like structure. While similar grid patterns canalso be formed in metallic sheets by stamping operations, these methodsproduce a significant amount of waste material. By comparison, theexpanded metal process disclosed herein essentially produces a metallicarticle having specifically designed openings or holes without removingany material to produce them. The resulting expanded metal can be takenup in rolls and subsequently cut into specific sized free-standingpieces for various applications.

The expanded metal article used in the present methods can comprise anymetal, for instance a conductive metal, that can be formed into a gridusing the expanded metal process. For example, the expanded metalarticle may comprise nickel, copper, aluminum, silver, palladium,platinum, titanium, or galvanized or stainless steel. Alloys of thesemetals can also be used. In some embodiments, the expanded metal articlecomprises copper, and is a copper grid.

The expanded metal article comprises a plurality of first segmentsintersecting a plurality of second segments forming an opening, and theshape of the opening is not particularly limited. For example, theopenings in the article can be diamond shaped, square, hexagonal, ovoid(having an shape similar to an egg or oval), or circular. These shapesmay also be elongated, depending on the directionality of the process bywhich the openings are formed and expanded. Also, irregular shapes arealso possible, depending, for example, on how the slit in the startingmetallic sheet is created and expanded. The size of the opening and thesize of the first and second elements can also vary, depending, forexample, on which side of the semiconductor material the expanded metalarticle is to be electrically coupled, described in more detail below.For example, the opening can have a dimension (such as a length or awidth) of from about 2 mm to about 20 mm. As a specific example, theexpanded metal article can comprise diamond shaped openings having awidth of from about 2 mm to about 10 mm, such as about 3 mm to about 7mm, and a length of from about 5 mm to about 20 mm, such as about 10 mmto about 15 mm. Furthermore, the first and second segments can have awidth of from about 0.5 mm to about 10 mm, including from about 1 mm toabout 5 mm. Thinner segments can also be used, as long as the expandedmetallic article remains as a continuous grid during handling.

The thickness of the expanded metal article can also vary depending on,for example, cost, handling characteristics, the thickness of themetallic sheet from which it was made, as well as the desired electricalcurrent carrying needs of the resulting photovoltaic cell. For example,the expanded metal article can have a thickness of from about 25 micronsto about 300 microns, including from about 50 microns to about 200microns and from about 75 microns to about 150 microns. Thinner expandedmetal articles can be used for highly conductive metals withoutsacrificing photovoltaic performance, while relatively thicker articlescan be used for metals with poorer mechanical strength but lower cost(including processing costs).

In some embodiments, the expanded metal article further comprises aplurality of soldering points which are configured to enable the metalarticle to be electrically coupled to a semiconductor material to form aphotovoltaic cell. The soldering points can be located at variouspositions on either the top or bottom surface of the expanded metalarticle and can comprise any soldering material known in the art. Forexample, the soldering points may be solder pads having, for example,square, rectangular, or round shapes, and these pads can be positionedon the intersecting first and second elements or at the intersection ofthese elements. Alternatively, or in addition, the soldering pointscomprise areas of higher amounts of solder compared to the rest of thesurface of the expanded metal article. For example, the surface of anexpanded copper metal article to be coupled to the semiconductormaterial may be coated by a layer of solder having a thickness of fromabout 1 to about 10 microns, such as from 2 to about 5 microns, whichcan be used, for example, to help prevent copper electromigration, andfurther may include a plurality of locations comprising solder having athickness of from about 15 to about 30 microns, such as from about 20 toabout 25 microns. In an example embodiment, the expanded metal articlemay be coated with an initial layer of solder coating, such as byelectroplating. The solder coating may have a thickness of, for example,from about 1 to about 10 microns, or from 2 to about 5 microns.Additional solder may then be applied onto the solder coating to preparefor soldering which electrically couples the expanded metal article tothe semiconductor material. The additionally applied solder may besupplied from, for example, a solder ribbon or a solder paste that canbe applied during any point in the assembly process. For example, theapplied solder can be solder pads that are formed on the expanded metalarticle prior to placing the metal article onto the semiconductormaterial. Alternatively, the solder pads created by the applied soldercan be added during or after the placement of the expanded metal articleonto the semiconductor material. For any of these soldering embodiments,flux may also be applied during the soldering process according tostandard techniques.

A specific example of an embodiment of the expanded metal article usedin the present methods is shown in FIG. 1. It should be apparent tothose skilled in the art that the figures presented are merelyillustrative in nature and not limiting, being presented by way ofexample only. Numerous modifications and other embodiments are withinthe scope of one of ordinary skill in the art, given the benefit of thepresent disclosure, and are contemplated as falling within the scope ofthe present disclosure. In addition, those skilled in the art shouldappreciate that the specific configurations are exemplary and thatactual configurations will depend on the specific system. Those skilledin the art will also be able to recognize and identify equivalents tothe specific elements shown, using no more than routine experimentation.

As shown in FIG. 1, expanded metal article 10 comprises a plurality offirst elements 11 intersecting a plurality of second elements 12,forming a continuous grid or mesh structure having a plurality ofopenings 13, which, in this example, are diamond shaped. In addition,expanded metal article 10 further comprises a plurality of solder pads14, which, as shown, are positioned around the surface of expanded metalarticle 10 at intersection points on the periphery of the surface aswell as in interior locations.

As described above, methods of the present disclosure compriseelectrically coupling or attaching the expanded metal article to asemiconductor material, such as amorphous silicon, crystalline silicon(including multicrystalline and monocrystalline silicon), or any othersemiconductor material suitable for use in a photovoltaic cell. Thesemiconductor material can vary in size and shape and can comprise, forexample, a square multicrystalline silicon cell or a monocrystallinesilicon cell having rounded corners, sometimes referred to as apseudosquare shape. Others will be known in the art.

The semiconductor material has a top surface, which is the lightincident surface of the photovoltaic cell to be formed, and a bottomsurface, which is the opposite side of the cell not exposed to light,and the expanded metal article can be electrically coupled to eithersurface. While the coupling can occur anywhere on the surfaces of eitherthe expanded metal article or the semiconductor material, in someembodiments the metallic article and semiconductor material coincide,with the expanded metal article substantially spanning a surface, suchas the top or bottom surface, of the semiconductor material. However, itis also possible for the expanded metal article to extend beyond thesemiconductor surface, thereby forming an interconnection element thatcan be used to connect multiple photovoltaic cells together to form amodule. At least one surface of the semiconductor material comprises aplurality of points of contact for the expanded metal article. In someembodiments, a majority of the soldering points on the surface of theexpanded metal article are electrically coupled and, as such, are inelectrical contact with, the plurality of points of contact on thesemiconductor material. That is, the majority of the plurality of solderpads on the surface of the expanded metal article are electricallycoupled at a plurality of soldering locations with the plurality ofsilver pads on the surface of the semiconductor material.

The points of contact on the surface of the semiconductor material willdepend, for example, on which surface the metallic article is coupled.In one embodiment, the top surface of the semiconductor materialcomprises a plurality of silver segments, and the expanded metal articleis coupled to these segments. The plurality of silver segments can be,for example, a linear array of parallel silver fingers traversing thetop surface of the semiconductor material from one edge to an oppositeedge. Such an arrangement is common and well known in photovoltaiccells. Alternatively, the silver segments can be linear segments ofsilver arranged linearly across the semiconductor surface, forming, forexample, broken parallel silver lines or fingers traversing from oneedge of the surface to an opposite edge. Other arrangements are alsopossible and will be known to one skilled in the art.

For this embodiment, since the top surface will be exposed to light, itis important that the expanded metal article have opening sizes andsegment widths that minimize shading to the semiconductor surface andthus has a high percent open area (which is the percentage of thesemiconductor material not shaded by the metallic article). Theresulting photovoltaic cell of this embodiment has a percent open areagreater than about 90%, such as greater than about 93%, or such asgreater than about 95%.

In another embodiment of the present methods, the expanded metal articleis electrically coupled to the bottom surface of the semiconductormaterial, which comprises a plurality of silver pads as the points ofcontact. The silver pads can be any shape, such as, for example, square,rectangular, or round, and may be the same or different in size and/orshape than the solder pads on the surface of the expanded metal article.The silver pads can be positioned anywhere around the bottom surface ofthe semiconductor material, including in an evenly distributed regulararray. Additional silver pads may be positioned around the edges of thesemiconductor material, thereby ensuring a secure contact.

For this embodiment, since the bottom surface of the semiconductormaterial will not be exposed to light, constraints relating to shadingcan be relaxed compared to the requirements of the top surface. Thus,opening sizes and segment widths of the expanded metal article can belarger for this embodiment and the percent open area can be less. Forexample, the resulting photovoltaic cell of this embodiment has apercent open area greater than about 80%, such as greater than about85%, or such as greater than about 90%.

Specific examples of the resulting photovoltaic cells produced in themethod of the present disclosure are shown in FIG. 2 and FIG. 3. Thus,in FIG. 2, expanded metal article 20, comprising a plurality of solderpads 24, is shown electrically coupled to the top surface ofsemiconductor material 25, which comprises a plurality of silversegments 26. Also, in FIG. 3, expanded metal article 30, comprising aplurality of solder pads 34, is shown electrically coupled to the bottomsurface of semiconductor material 35, comprising a plurality of squaresilver pads 37. As can be seen in FIGS. 2 and 3, a majority of solderpads 24 and 34 are in electrical contact with silver segments 26 orsilver pads 37, respectively, where the locations of electrical contactare soldering locations at which the expanded metal article 20 or 30 areelectrically coupled to the semiconductor material 25 or 35.

As discussed above, one or both surfaces of the semiconductor materialis electrically coupled with the expanded metal article. If only onesurface is used, the other surface can be coupled using any known methodto complete the circuit in the photovoltaic cell. For example, in thepresent methods, a free-standing metallic article that differs from theexpanded metal article, can be electrically coupled to the availablesemiconductor surface to form the photovoltaic cell. In particular, ametallic article comprising a plurality of electroformed elementsinterconnected to form a unitary, free-standing piece comprisinggridlines can be used, such as those described in U.S. Pa. Nos.8,569,096 and 8,936,709.

FIGS. 4A-4B illustrate further embodiments in which the expanded metalarticles of the present disclosure include a plurality of cuts toaccommodate a difference in coefficient of thermal expansion between theexpanded metal article and the semiconductor material. FIG. 4A is a fullview of an expanded metal article 40, while FIG. 4B is a detailed view.The expanded metal article 40 has a plurality of intersecting firstsegments 41 and a plurality of second segments 42 that form a pluralityof openings 43 as described above for previous embodiments. The metalarticle 40 also has a plurality of cuts 44 that form discontinuities inthe grid, where each cut 44 extends across at least one of the firstsegments 41, one of the second segments 42, and/or an intersection ofone of the first segments 41 and one of the second segments 42. In themetal article 40 of FIGS. 4A-4B, each cut 44 is depicted as extendingacross two intersections of the first segments 41 and second segments42; however, other lengths of cuts 44 are possible.

The plurality of cuts 44 allow portions of the metal article 40 tofreely expand and contract, and provide mechanical flexion within themetal article 40, thus relieving thermal stresses induced during bondingof the metal article to the semiconductor wafer. In the embodiment ofFIGS. 4A-4B, the cuts 44 are arranged as an orthogonal array, withdimensions of the array chosen to accommodate a difference incoefficient of thermal expansion between the expanded metal article andthe semiconductor material. For instance, array dimensions may include alateral spacing 46 of about 10 to 15 mm and a lengthwise spacing 47(from the end of one cut to the start of the next cut) of about 3-7 mmfor a 156 mm by 156 mm photovoltaic cell. Instead of an orthogonal arraywhere the cuts 44 are aligned horizontally and vertically with eachother, the array may be a staggered array in which the cuts 44 arediagonally aligned with each other. Other array layouts are alsopossible, which could include having arrays of cuts 44 only in certainregions of the metal article 40, such as where higher stresses areexpected. Furthermore, the cuts 44 need not be arranged in an array,such as being randomly placed across the metal article 40. Arraydimensions may be uniform throughout the array, or may be different incertain regions such as near the perimeter of the metal article 40.

The array dimensions also include the dimensions of the cuts 44, wherefor a 156 mm by 156 mm photovoltaic cell the cuts 44 may have a length48 ranging from, for example, 3 to 7 mm, and a width 49 ranging from,for example, 0.1 to 1 mm. Note that the endpoints of the lengths 47 and48 are denoted as being from the center of each opening 43 in thisembodiment, although other conventions may be utilized as desired forspecifying the dimensions of the cuts 44. The specific geometricalarrangement of the plurality of cuts 44 and dimensions of the array ofcuts are chosen based on the specific materials being used for thephotovoltaic cell and the temperature ranges to which the materials areanticipated to be exposed.

In addition to the thermal expansion stresses, the semiconductormaterial may also experience mechanical stresses imposed by aninterconnect and/or a metallic article that serves as an electricalconduit attached to the front (i.e., top) surface of the semiconductor.These mechanical stresses can cause the semiconductor wafer to warp orbow. The specific arrangement of cuts in the expanded metal article onthe back (i.e., bottom) surface of the semiconductor can also be chosento balance out these mechanical stresses, thereby enabling thesemiconductor to remain flat. That is, in some embodiments the pluralityof cuts is arranged to relieve mechanical stresses induced by themetallic article on the top surface. The number, density, orientation,and location of cuts can vary depending on the location and magnitude ofstress to be counter-balanced. For example, the overall number, density,and/or size of the cuts can be increased for instances in which higherstresses are anticipated, such as in aerospace applications due to theextreme environmental conditions. In another example, the direction(i.e., orientation) of the cuts can be arranged according to thedirection of the stresses that are to be relieved. Furthermore, as thedistribution of stresses imposed on the semiconductor is likely to bespatially asymmetric with respect to the location on the semiconductor,the number, size, orientation, and density of cuts can be tailored tobalance out these regional stresses. For example, higher stress can beincurred on the corners and edges of the semiconductor due togeometrical effects. To counter-balance these stresses, a greaterdensity of cuts or larger sized cuts may be placed at the corners andedges of the expanded metal article to give additional stress relief.

FIG. 5 shows a photovoltaic cell 50 onto which the expanded metalarticle 40 with cuts 44 has been mounted. FIG. 5 depicts solderinglocations 52, which are linear paths across a length of the photovoltaiccell 50 in this embodiment. At least some of the plurality of cuts 44are between neighboring soldering locations; that is, being bordered bythe nearest two soldering locations 52. For example, in FIG. 5 the cuts44 are perpendicular to the linear soldering locations 52 and extendacross a majority of the distance between the soldering lines. As anexample embodiment, for a spacing of about 15 mm between the solderinglines (locations) 52, the cuts may extend approximately 10 to 13 mmacross that distance. In other embodiments, the cuts 44 span variousportions of the distances between soldering locations, and may be at anyorientation with respect to the soldering locations 52, such asparallel, perpendicular, or any angle between. In some embodiments, thecuts 44 do not necessarily need to all be between soldering points(soldering locations 52). However, the cuts 44 that are betweensoldering locations 52 provide stress relief by allowing the expandedmetal article, solder, and the semiconductor wafer to expand andcontract relative to each other, compared to the fixed points where themetal article 40 is joined to the photovoltaic cell 50.

FIG. 6 is a perspective view of an example metal cutting assembly 60that may be used to create cuts within the expanded metal article. Metalcutting assembly 60 includes a cutting tool 62, a holding plate 64, anda receiving plate 66, where the holding plate 64 is stacked between thecutting tool 62 and the receiving plate 66. Cutting tool 62 has aplurality of cutting elements 63 facing holding plate 64, where thecutting elements 63 serve as knife blades that pierce through theexpanded metal article to form cuts (e.g., cuts 44 of FIG. 4). Thecutting elements 63 may be made of, for example stainless steel. Inoperation, the cutting tool 62, holding plate 64, and receiving plate 66are pressed together, such as by manual or automatic actuation.

FIGS. 7-9 show stages of forming the cuts in the expanded metal articleusing the metal cutting assembly 60. An expanded metal article 70 isprovided, such as being supplied from a roll of expanded mesh material,or alternatively supplied as an individual piece. Next, as shown in FIG.7, an expanded metal article 70 is inserted between the holding plate 64and the receiving plate 66. In FIG. 8, the holding plate 64 is loweredto hold the expanded metal article 70 between the holding plate 64 andthe receiving plate 66. The cutting tool 62 is then lowered as indicatedby arrows 80, such that the cutting elements 63 penetrate through theholding plate 64 and the receiving plate 66 and form a plurality of cuts74 in the expanded metal article 70, as shown in FIG. 9. In someembodiments, the holding plate 64 and receiving plate 66 may be made ofa metal such as stainless steel or aluminum, having pre-formed apertures65 through which the cutting elements 63 can extend. In otherembodiments, the holding plate 64 and receiving plate 66 may be made ofa material that the cutting elements can pierce, without requiringpre-formed apertures. The cutting tool 62 is then raised while theholding plate 64 remains in place, with the metal article 70 sandwichedbetween the holding plate 64 and receiving plate 66, to assist inseparating the cutting elements 63 from the expanded metal article 70and to prevent the expanded metal article 70 from deforming as thecutting elements 63 are removed.

In some embodiments, the process can also involve a sizing tool—as partof or as a separate component from the metal cutting assembly 60—to trimthe outer perimeter of the expanded metal article 70 to the necessarysize and shape for a photovoltaic cell. For example, the length and/orwidth of the overall expanded metal article can be cut to approximately156 mm for a 156 mm² photovoltaic cell. If the expanded mesh materialfor the metal article is supplied from a roll, the roll may bepre-fabricated to 156 mm such that only one end of the mesh materialneeds to be cut to length. Additionally, for a monocrystalline cell thesizing tool may be configured to create the corners 75 of thepseudosquare shape while the expanded metal article 70 is held in themetal cutting assembly 60.

FIG. 10 is a flowchart 100 of methods for forming a photovoltaic cell inaccordance with embodiments of the present disclosure. In step 110, anexpanded metal article is provided, having a plurality of first segmentsintersecting a plurality of second segments forming a plurality ofopenings. In some embodiments, the expanded metal article has a surfacecomprising a plurality of solder pads.

In some embodiments, the expanded metal article has a plurality of cuts,such as created by a metal cutting assembly provided in step 120. Eachcut in the plurality of cuts creates a discontinuity in the expandedmetal article. That is, the cuts are breaks in the first segments and/orsecond segments that allow strain within the metal article or within thephotovoltaic cell assembly to be relieved. The metal cutting assemblyincludes a cutting tool, a receiving plate, and a holding plate. Theholding plate is stacked between the cutting tool and the receivingplate, and the cutting tool comprises a plurality of cutting elementsfacing the holding plate. After the expanded metal article is providedin step 110, the expanded metal article is inserted between the holdingplate and the receiving plate. The cutting tool is moved toward theholding plate and the receiving plate, as described in FIGS. 6-9, suchthat the plurality of cutting elements penetrates through the holdingplate and the receiving plate and forms a plurality of cuts in theexpanded metal article.

In step 130, a semiconductor material is provided, where thesemiconductor material has a top surface that serves as a light-incidentsurface of the photovoltaic cell, and a bottom surface opposite the topsurface. In step 140, the expanded metal article is electrically coupledwith the semiconductor material at a plurality of soldering locations.For example, the expanded metal article is electrically coupled to aplurality of silver pads on the bottom surface of the semiconductormaterial. In embodiments in which the expanded metal article is providedwith solder pads, a majority of the plurality of solder pads on thesurface of the expanded metal article is electrically coupled with theplurality of silver pads on the bottom surface of the semiconductormaterial at a plurality of soldering locations. In some embodiments, theexpanded metal article has a solder coating, and the electrical couplingof step 140 involves soldering the expanded metal article to theplurality of silver pads with an applied solder that is placed onto thesolder coating.

In embodiments in which the expanded metal article has cuts for thermalor mechanical relief, at least one cut in the plurality of cuts iswithin a region between neighboring soldering locations of the pluralityof soldering locations. The plurality of cuts, can be arranged as anarray having array dimensions configured to accommodate a difference incoefficient of thermal expansion between the expanded metal article andthe semiconductor material.

The present disclosure further relates to photovoltaic cells produced bythe methods described above. The photovoltaic cell comprises an expandedmetal article electrically coupled to a surface of a semiconductormaterial. The expanded metal article comprises a plurality of firstsegments intersecting a plurality of second segments forming an openingand further comprises a plurality of soldering points, such as solderpads, and the semiconductor material comprises a plurality of points ofcontact for the expanded metal article. The expanded metal article andsemiconductor material can be any of those described above. In oneembodiment, the semiconductor material has a top or light incidentsurface comprising a plurality of silver segments, such as silverfingers, and a majority of the plurality of solder pads on the surfaceof the expanded metal article is in electrical contact with theplurality of silver segments on the semiconductor material. In a secondembodiment, the semiconductor material has a bottom or non-lightincident surface comprising a plurality of silver pads, and a majorityof the plurality of solder pads on the surface of the expanded metalarticle is in electrical contact with the plurality of silver segmentson the semiconductor material.

In certain embodiments of photovoltaic cells of the present disclosure,an expanded metal article comprises a plurality of first segmentsintersecting a plurality of second segments forming a plurality ofopenings. The expanded metal article further comprises a plurality ofcuts, each cut in the plurality of cuts extending across an intersectionof one of the first segments and one of the second segments. Asemiconductor material has a bottom surface comprising a plurality ofsilver pads, where a top surface of the semiconductor material serves asa light-incident surface of the photovoltaic cell. The expanded metalarticle is electrically coupled at a plurality of soldering locations tothe plurality of silver pads on the surface of the semiconductormaterial. A free-standing metallic article is electrically coupled withthe top surface of the semiconductor material to form the photovoltaiccell.

Various combinations and embodiments described above relating to themethods of the present disclosure can also relate to the photovoltaiccells of the present disclosure. The resulting cells can be coupled toform photovoltaic modules.

While the specification has been described in detail with respect tospecific embodiments of the invention, it will be appreciated that thoseskilled in the art, upon attaining an understanding of the foregoing,may readily conceive of alterations to, variations of, and equivalentsto these embodiments. These and other modifications and variations tothe present invention may be practiced by those of ordinary skill in theart, without departing from the scope of the present invention, which ismore particularly set forth in the appended claims. Furthermore, thoseof ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention.

What is claimed is:
 1. A method for forming a photovoltaic cell, themethod comprising: a) providing an expanded metal article comprising aplurality of first segments intersecting a plurality of second segmentsthereby forming a plurality of openings, the expanded metal articlehaving a surface comprising a plurality of solder pads; b) providing asemiconductor material having a bottom surface comprising a plurality ofsilver pads, wherein a top surface of the semiconductor material servesas a light-incident surface of the photovoltaic cell; and c)electrically coupling, at a plurality of soldering locations, a majorityof the plurality of solder pads on the surface of the expanded metalarticle with the plurality of silver pads on the bottom surface of thesemiconductor material.
 2. The method of claim 1, wherein the expandedmetal article spans the bottom surface of the semiconductor material. 3.The method of claim 1, wherein each opening in the plurality of openingsis diamond shaped, each opening having a width from 3 mm to 7 mm, and alength from 10 mm to 15 mm.
 4. The method of claim 1, wherein each ofthe first segments and each of the second segments have a width from 1mm to 5 mm.
 5. The method of claim 1, wherein the expanded metal articlehas a thickness from 75 microns to 150 microns.
 6. The method of claim1, wherein the photovoltaic cell has a percent open area greater than80%.
 7. The method of claim 1, wherein the expanded metal articlecomprises an interconnection element that extends beyond the bottomsurface of the semiconductor material.
 8. The method of claim 1, whereinthe method further comprises electrically coupling a free-standingmetallic article with the top surface of the semiconductor material toform the photovoltaic cell, wherein the metallic article comprises aplurality of electroformed elements interconnected to form a unitary,free-standing piece comprising gridlines.
 9. The method of claim 1,further comprising: a1) providing a metal cutting assembly, the metalcutting assembly comprising a cutting tool, a receiving plate, and aholding plate, the holding plate stacked between the cutting tool andthe receiving plate, wherein the cutting tool comprises a plurality ofcutting elements facing the holding plate; a2) after the step (a) ofproviding the expanded metal article, inserting the expanded metalarticle between the holding plate and the receiving plate; and a3)moving the cutting tool toward the holding plate and the receiving platesuch that the plurality of cutting elements penetrates through theholding plate and the receiving plate and forms a plurality of cuts inthe expanded metal article.
 10. The method of claim 9, wherein at leastone cut in the plurality of cuts is within a region between neighboringsoldering locations of the plurality of soldering locations.
 11. Themethod of claim 9, wherein each cut in the plurality of cuts creates adiscontinuity in the expanded metal article.
 12. The method of claim 9,wherein the plurality of cuts is arranged as an array having arraydimensions configured to accommodate a difference in coefficient ofthermal expansion between the expanded metal article and thesemiconductor material.
 13. The method of claim 9, wherein: the methodfurther comprises electrically coupling a free-standing metallic articlewith the top surface of the semiconductor material to form thephotovoltaic cell, wherein the metallic article comprises a plurality ofelectroformed elements interconnected to form a unitary, free-standingpiece comprising gridlines; and the plurality of cuts is arranged torelieve mechanical stresses induced by the metallic article on the topsurface of the semiconductor material.
 14. A method for forming aphotovoltaic cell, the method comprising: a) providing an expanded metalarticle comprising a plurality of first segments intersecting aplurality of second segments thereby forming a plurality of openings,wherein the expanded metal article further comprises a plurality ofcuts, each cut in the plurality of cuts creating a discontinuity in theexpanded metal article; b) providing a semiconductor material having abottom surface comprising a plurality of silver pads, wherein a topsurface of the semiconductor material serves as a light-incident surfaceof the photovoltaic cell; and c) electrically coupling the expandedmetal article at a plurality of soldering locations to the plurality ofsilver pads on the bottom surface of the semiconductor material, to formthe photovoltaic cell.
 15. The method of claim 14, wherein: the expandedmetal article comprises a solder coating; and the electrically couplingof step (c) comprises soldering the expanded metal article to theplurality of silver pads with an applied solder that is placed onto thesolder coating.
 16. The method of claim 14, wherein at least one cut inthe plurality of cuts is within a region between neighboring solderinglocations of the plurality of soldering locations.
 17. The method ofclaim 14, wherein the plurality of cuts is arranged as an array havingarray dimensions configured to accommodate a difference in coefficientof thermal expansion between the expanded metal article and thesemiconductor material.
 18. The method of claim 14, further comprising:a1) providing a metal cutting assembly, the metal cutting assemblycomprising a cutting tool, a receiving plate, and a holding plate, theholding plate stacked between the cutting tool and the receiving plate,wherein the cutting tool comprises a plurality of cutting elementsfacing the holding plate; a2) after the step (a) of providing theexpanded metal article, inserting the expanded metal article between theholding plate and the receiving plate; and a3) moving the cutting tooltoward the holding plate and the receiving plate such that the pluralityof cutting elements penetrates through the holding plate and thereceiving plate and forms the plurality of cuts in the expanded metalarticle.
 19. A photovoltaic cell comprising: an expanded metal articlecomprising a plurality of first segments intersecting a plurality ofsecond segments forming a plurality of openings, wherein the expandedmetal article further comprises a plurality of cuts, each cut in theplurality of cuts creating a discontinuity in the expanded metalarticle; and a semiconductor material having a bottom surface comprisinga plurality of silver pads, wherein a top surface of the semiconductormaterial serves as a light-incident surface of the photovoltaic cell;wherein the expanded metal article is electrically coupled at aplurality of soldering locations to the plurality of silver pads on thebottom surface of the semiconductor material.
 20. The photovoltaic cellof claim 19, wherein a free-standing metallic article is electricallycoupled with the top surface of the semiconductor material to form thephotovoltaic cell.